Photoresist dry films have been developed for use in lithographic processes in the manufacture of integrated circuits. Use of dry film photoresist has become particularly critical in the manufacture of large scale integration (LSI) and very large scale integration (VLSI) devices. Commercially available forms of this film are manufactured by companies such as the Dynachem and Dupont Corporations, and are characterized as being easily contaminated, tacky and limp. Although tacky, these films are "peelable", making it possible to package them with protective cover films such as Mylar.TM., polyethylene, or polyolefin to insure the integrity of the photoresist film during handling. Mylar is a trademark of the E.I. Dupont de Nemours Co.. The photoresist manufactured by Dynachem, for instance, is packaged between polyethelene layers and rolled into spools. The photoresist manufactured by Dupont, alternatively, is packaged in multi-layer rolls wherein the photoresist is sandwiched between a Mylar top layer and a polyolefin bottom layer.
For use in lithographic processes, the dry film resist must be uniformly laminated to the substrate under manufacture. This is typically done with a lamination process, but in order to utilize the previously described rolled dry film resists products, the resist material must both be separated from the protective layer(s) and laminated to the substrate. The lamination processes is further complicated by the fact that semiconductor wafers are circular in shape whereas the resist is rolled out as a continuous sheet which is rectangular in shape.
A prior technique utilized to apply photoresist to substrates is described in U.S. Pat. No. 4,495,014 (Gebrian, et al.). Gebrian, et al. discloses a process of laminating under pressure a section of supported photoresist material to a moving sheet substrate, releasing the lamination pressure, removing the support from the laminated layer and thereafter trimming the photoresist layer to conform to the profile of the sheet substrate.
The process disclosed in Gebrian, et al. is unacceptable for semiconductor wafers because the trimming process is restricted to trimming the photoresist material to the outside profile of rectangular substrates. In semiconductor wafer processing, a non-exclusion area (typically 3 millimeters) within the outside diameter of the wafer is required for handling of the wafer. This means that the resist material must be trimmed in a circular pattern within the outside diameter of the wafer.
The prior technique for placing dry film resist on circular wafers was to laminate the resist to the wafer, and then trim the resist into a circular pattern inside the outer diameter of the wafer. The trimming process included either trimming with a laser or a sharp edge, such as a knife. Laser cutting is unacceptable because the heat produced from the process tends to bond the plastic protective layer to the wafer. Likewise, knife cutting processes are unacceptable because they cause a great deal of structural damage to the wafer and the resultant patterns are not dimensionally accurate.
An apparatus which automatically and accurately laminates circular dry film resist patterns to semiconductor wafers, is therefore highly desirable.